In internal combustion engines and especially spark ignition engines, the fuel quantity supplied for combustion is adjusted as a function of an inducted air mass (air volume). The supplied air volume is controlled by what is commonly known as the throttle valve, which is controlled directly or via a control as a function of the gas pedal position (driver's desired torque). A desired air charge in the combustion chamber, from which a desired throttle valve position is determined and is then adjusted to the desired position by a controller, corresponds to the gas pedal position. The resulting air volume in the combustion chamber (of a cylinder) of the internal combustion engine is adjusted via sensors and suitable control methods.
For each combustion cycle, the existing air mass (in the combustion chamber) is determined by charge sensing.
In a charge sensing system, what is referred to as the α-n system, the fresh-air flow rate is determined via a characteristics map as a function of the throttle-valve angle α and speed n and is then converted into an actual air-mass flow.
Via a control model (for example, a throttle valve model) with the aid of the pressure drop across the throttle valve, as well as the temperatures in the intake manifold, and with the aid of the throttle-valve angle, the air-mass flow is calculated in what is referred to as the p-n system. The inducted fresh air (air volume in the combustion chamber) is thereby computed taking into account engine speed n, pressure p in the intake manifold (upstream of the intake valve), the temperature in the intake port, and other influences (camshaft control and valve stroke control, intake-manifold switchover, position of the charge-turbulence flaps).
A further method employs a hot-film air-mass meter (HFM) that determines the air mass flow streaming into the intake manifold.
However, only during steady-state engine operation, do the α-n system and the HFM system, which each determine only the mass flow streaming through the intake manifold, provide a valid value for the actual cylinder charge or, respectively, for the air volume that is available for the combustion. In response to a load change, i.e., a sudden change in the throttle-valve angle, the mass flow in the intake manifold changes immediately, while the mass flow entering into the cylinder (combustion chamber) and thus the cylinder charge only changes in response to an increase or decrease in the intake manifold pressure.
To correctly determine the charge influencing quantities over time, conventional approaches for determining the air mass during load change are based on the load build-up and reduction (load change) dynamics being retarded (delay of the throttle valve adjustment) to still be able to determine the air volume accurately enough. However, such a delay in throttle valve movement leads to a slower load build-up (or load reduction) of the vehicle and thus to an unwanted, reduced load change dynamics.
There are other approaches for offsetting this reduced dynamics—especially upon acceleration—by compensating for the inaccurately computed air volume by injecting fuel multiple times. However, this requires complex modifications in the injection control system.
Another problem is that the actual air charge in the combustion chamber is not established until after the intake valve is closed. At that time point, however, to ensure an efficient mixing of the air-fuel mixture, fuel is no longer being injected into the combustion chamber itself (direct injection) or into the intake manifold (manifold injection). In manifold injection, the injection can even be already ended before the intake valve opens at all.
To overcome this problem in intake manifold injection systems, the German Patent Application DE 10 2005 059 436 A1 describes an approach for predicting the actual air charge in the combustion chamber. In this regard, using a pressure gradient in the manifold and predicted throttle valve positions, the approach provides for computing the manifold pressure at the instant of intake valve closing and consequently a predicted air charge in a plurality of stages.
A refined manifold injection system approach is based on using the position controller of the throttle valve to acquire an actual quantity (actual air charge) from a setpoint variable (desired air charge). During dynamic operation (in the case of a load change), a setpoint variable in advance of an actual quantity is thereby used for predicting the actual quantity. Attenuation and retardation are used to convert the leading signal into a lagging signal. However, when working with internal mixture formation (in the case of direct injection), accurate fuel metering requires that the air volume contained in the combustion chamber be determined as exactly as possible prior to the actual injection, to make possible a high load change dynamics.